Automotive electronic circuits are subject to severe EMI due to noise from ignition circuits and many other sources on or off the vehicle. Hybrid electronic modules are produced typically with plastic molded packages. The plastic does not protect the internal electronic circuitry from external radio frequency (RF) energy. RF currents flow along the connecting harness to the hybrid module. Capacitive coupling between the module and its surroundings completes the path for the RF current flow.
Large hybrid components with metallic mounting plates can readily allow RF currents to flow through and away from the module to adjacent structures. Smaller modules without metallic plates will depend solely on capacitive coupling from its internal components for completion of the current path, thus all parts of the substrate become a radiator for RF energy.
Presently many small modules such as pressure transducers utilize capacitors and a grounded metallized back plane to control the flow of RF energy on the substrate of the module. The backplane and capacitors have a connection to the negative power lead (ground) at the connector. Such techniques afford limited immunity to electromagnetic interference (EMI); in some applications an incremental improvement in immunity is required.
The traditional techniques for improving such performance often carry severe cost penalties. It is also known to completely shield the front of the circuit as well as the backplane; this too is expensive to implement. Accordingly it is desired to improve the EMI (or RF) immunity at low cost and in keeping with conventional packaging and without increasing package size.